The present invention relates to a data transfer apparatus, and more particularly to a data transfer apparatus suitable for performing data transfer between input/output (I/O) devices and a main storage unit.
An old stand-alone type channel device such as an IBM 2880 Block Multiplexer Channel has given way to a recent so-called, concentrated type channel device such as that disclosed in U.S. Pat. No. 4,272,815 (JP-B-58-6173). A concentrated type channel device is of great advantage due to miniaturization of its dimensions.
However, with a conventional concentrated type channel system, there are some disadvantages associated with (1) the processing capability of a common control unit and (2) adverse effects of the common control unit upon a plurality of channels at a time regardless of the essential independence of each individual channel.
Specifically, as to the former disadvantage (1), a data transfer between a concentrated type channel device and a common control unit is time-divisionally performed in units of one or two bytes which is the byte length for use in data transfer between the channel device and the common control unit. The common control unit collects 32 bytes of data from the channel device at the transfer rate of 1 or 2 bytes per transfer. The 32 byte unit collected device in units of 32 bytes, which is the byte length for use in data transfer between the common control unit and a main storage unit. The common control unit delivers the 32-byte data to the main storage unit. Consequently, the greater the number of channel devices to be controlled and the more the data transfer rate of each channel device becomes quick, the more difficult it becomes to improve the performance of the system due to the data transfer rate between the common control unit and the channel device.
As to the second disadvantage, since the common control unit collectively fetches data from a plurality of channel devices, any trouble in a circuit portion (data buffer) of the common control unit functioning to collectively fetch the data causes an adverse effect upon the plural channel devices at the same time.